Electric discharge tube comprising a directional electron beam



Sept. 19, 1950 J. DE GIER ELECTRIC DISCHARGE TUBE COMPRISING A DIRECTIONAL ELECTRON BEAM I Filed July 29. 1948 7 9 1 j j v/ x E Q 1 Z 6 j 'g JUHANJVFSDE GIER IN V EN TOR.

F 2 Q L AGENT.

Patented Sept. 19, 1950 UNITED STATE ELECTRIC DISCHARGE TUBE oMPRIsINC,

A DIRECTIONAL ELECTRONBEAM: Johannes dc Gier, Eindhoven, Netherlands, as-

signor to Hartford National Bank andiTrust Company, Hartford, Conn.,.as trustee" Application July 29, 948, Serial No. 41,364 In the Netherlands September 12, 1941 In electricdischarge tubes comprising a directional electron beam and intended vto reproduce 3Claims. (Cl. 250-162) television images, the electron beam produces a luminousspot on the screen. The latter may be either a luminescent screen or a thin metallic 1 plate which is locally heated. The light intensity oithe luminous spot increases, more particularly when use is made of a metal screen, as the accelerating voltage forthe electrons is chosen to be higher. '7

It causes difliculties toraise the accelerating voltage with unvaried diameter. of the tube. True the difficulties'may be materially reduced by increasing the diameter of that portion of the tube in which the field electrodes are housed, but it is undesirable to increase the diameter of the tube in View of the increase in the diameter of the coils used for the electro-magnetic concentration and directioning of the beam and surrounding the tube. This would result in an increase of the energy necessaryto generate the required field intensity and hence in supply de vices of larger side.

The present invention relates to a device, the object of which is to raise th accelerating voltage to a considerable extent with unvaried diameter of atube.

One of the factors preventing an increaseof the accelerating voltage with the conventional arrangement of the electrode system on the-stem secured by sealing to the glass neck of the tube is that the insulated wall portion over which the potential distribution occurs, extends from the anode to beyond the cathode so that at the area of the electron-emissive surface of the cathode the wall exhibits a potential which is materially higher than that of the cathode; This is favour able for the production of irregular voltage divisions over the wall, which may bring aboutsliding-spark discharges and punctures'of the'wall. The irregular voltage distribution and the sliding spark discharges are brought about by the modifi:

cation of the uniform voltage distribution over the insulated wall by electrons which are freed from the surface area of the electrodes as a result of cold emission and which strike the wall of the tube.

According to the invention, the cathode is secured to a cylindrical insulator which fits in theglass neckof the tube, that surface of the in V sulator which is adjacent the wall being'covcred-with an adhesive conductive layer "which'is either connected tothe cathode or provided with a lead-out conductor. In the latter case the conductor is adapted to be connected to anearthed have a particularly disadvantageous consequence if they produce a high field-intensity in the vicinityof the cathodej The resulting forced discharge ofelectrons may cause an increase of the electron-emitting capacity of an oxide cathode such'that' the tube isithus rendered practically unserviceable. l

In previous cases attempts have been made to avoid irregularv charges of-the wall in high-tension discharge tubes by surrounding the discharge path by ametal screen. A known construction in whichthis screen is formed as a part of the wall does not enter into consideration in the present iinstance; i In a further known construction the screen is provided between the wall and the electrodes and is connected" to the anode. This construction has thedisadvantage that the diameter of the'tube is required to be considerably larger than that of th electrodes. Since the charge of the screen is carried ofi, there is, moreover, someielectron loss which has to be provided by the cathode of the tube, thus resulting in a higher load thereon.

in most cases of "a metal having a high work function, y a i In a patent application previously filed it is assumed that in electron-ray tubes comprising a directional electron'beamjwhich are surrounded by one'or more magnet coils for controlling the path of the electron rays and of which the diameter is thusrequired to beassmall as possible, electron emission phenomena on electrodes, where such is not desired. may be avoided with great security by the arrangement of a metal screen, insulated from the electrodes, between the wall and that field electrode which is most adjacent the cathode, which screen extends from the tube wall in'the space-intermediate the '"field electrodes and terminategtherein; and intersects the electron paths, which: otherwise would connect the field electrodes'with 'the wall. Electrons which .come:,-'available upon suchelectron-emission phenomena! and which follow paths ending .on the :Wallof the 'tube may release secondary electrons at the surfaceoi thewall and thus bring about potential'differences'sufficiently high to initiate an electric spark-discharge, If the lines of force along which the electrons travel terminate on a screen arranged in'an insulated manner, this screen'will be charged in a negative sense, so that further supply of electrons cannot take place.

The screen may itself exhibit a shape'which is as edv ii se s as. d si sjfcr' int cold emission, since it doesnot f ulfila functionin the electrode system for generatingthe electron beam.

This solution has been found to be not wholly only discharges the insulated screen but also causes a strong charge thereof in the opposite sense and hence strong electric fields between the screen and th cathode with the harmful consequence already previously referred to.

According to a further feature of the invention, 'in an electron-ray tube in which the electrode system is housed in the glass neck of the tube, the tube wall and that field electrode which is most adjacent the cathode are separated by.

a metal screen which extends from the wall in the space between the field electrodes and terminates therein and is connected in an electrically conductive manner to the conductive coating provided on the cathode insulator. In this case the electric charge supplied as a result of spark discharge is carried oil by the conductor connected to the conductive layer without any harmful efiect being possible.

The invention will now be explained more fully by reference to the accompanying drawing, showing one example of the part of a cathode-ray tube containing the electrode system, to whichthe invention is applied.

The "glass wall I surrounds the electron-emitting cathode 2 and -the accelerating anode 3. The

cathode 2 is secured to a cylindrical insulator 4 which fits in the glass neck of the tube and which may consist of ceramic material. The anode 3 is clamped in position in the tube by means of resilient members 5. A voltage difference of from 20,000'to 30,000 volts is applied between the cathode and the anode.

The insulating ring 4 also serves for the arrangement of the control electrode 6, to which a voltage is supplied which is adapted to vary between cathode potential and a negative value of a few hundred volts.

That surface of the ring 4 which is adjacent the wall of the tube is covered with an adhesive conductive layer 1 to which a supply conductor 8 is connected. This negative conductor may be connected to an earthed point of the source of high-voltage supply. Thus, in adetermined circuit in which the control voltage is supplied by way of a resistance connected inseries with the cathode, so that the negative voltage is produced as a voltage loss in this resistance and is obtained by the supply current of the device traversing the. resistance, the conductive layer exhibits the same potential as the control electrode. In other cases, in which a separate source of supply is used to provide the control voltage, the conductive layer maybe connected direct to the cathode as shown'in thedrawing.

- Theanode voltage applied to the tube during operation is set up between the conductive layer 1 and a conductive coating H] which is provided on the wall of the tube and engaged by'clamping springs for supporting the anode 3. A distribution of voltage along the wall of the tube which is as uniform as possible facilitates satisfactory operation of the tube and decreases therisk of disturbances. If, however, the wall of the tube is struck by electrons of, sufficient velocity t release secondary electrons, potential difierences may arise and lead to an increase of the voltage gradient along the surface of the wall. A- resultant voltage discharge will find a way from the conductive coating H] to the other pole of the high-tension unit. The arrangement of a metal screen 9, which extends from the wall in the space intermediate the field electrodes and terminates therein and is connected in an electrically conductive manner, to the conductive layer provided on the cathode insulator prevents the discharge from reaching the cathode. Although the risk of irregular charge of the wall is considerably reduced by the provision of the conductive layer on the surface of the cathode insulator adjacent the wall and the connection thereof with an earthed point of the high-tension source, the presence of the screen substantially avoids any detrimental consequences of a discharge, since the electric charge is in this case carried ofi by the shortest route without being capable of provoking undue field intensities in the vicinity of the cathode.

What I claim is:

1. .An electric discharge device comprising an envelope having a tubular wall portion, a cathode source for generating a directional electron beam, first and second field electrodes within said envelope, a cylindrical insulating member interposed between said cathode source and said tubular envelope portion and fixedly securing said cathode source in spaced relation to said field electrodes, an adhesive electrically conducting layer interposed between said cylindrical member and said tubular envelope portion, and means to couple said conducting layer to said cathode.

2. An electric discharge device comprising an envelope having a tubular wall portion, a cathode source for generating a directional electron beam, first and second field electrodes within said envelope, a cylindrical insulating member interposed between said cathode source and said tubular envelope portion and fixedly securing said cathode source in spaced relation to said field electrodes, an adhesive electrically conducting layer interposed between said cylindrical memberand said tubular envelope portion and directly connected to said cathode source.

3. An electric discharge device comprising an envelope'having a tubular wall portion, a cathode source for generating a directional electron beam, first and second field electrodes within said envelope, a cylindrical insulating member interposed between said cathode source and said tubular envelope portion and fixedly securing said cathode source in spaced relation to said field electrodes, an adhesive electrically coducting layer interposed between said cylindrical member and said tubular envelope portion, means to couple said conducting layer to said cathode, and a metal screening member extending from the said wall portion and interposed between the said field electrodes, said screening member bein electrically connected to said conducting layer.

' J OHAN'NES DE GIER.

REFERENCES CITED The following references are of record in the file of this patent:

Great Britain Mar. 18, 1949 

